Referring to FIG. 1, a turbine engine 10 is illustrated including a compressor section 12, a combustor section 14 and a turbine section 16. In the turbine section 16, there are alternating rows of stationary airfoils 18 (commonly referred to as vanes) and rotating airfoils 20 (commonly referred to as blades). Each row of blades 20 is formed by a plurality of airfoils 20 attached to discs 22 forming a rotor 24. The blades 20 extend radially outward from the discs 22 and terminate in a region known as the blade tip 26. Each row of vanes 18 is formed by attaching a plurality of vanes 18 to a vane carrier 28. The vanes 18 extend radially inwardly from an inner peripheral surface 30 of the vane carrier 28. The vane carrier 28 is attached to an outer casing 32 to form an outer casing structure 34, which encloses the turbine section 16 of the engine 10.
Between the rows of vanes 18, a ring seal assembly 36 can be attached to the inner peripheral surface 30 of the vane carrier 28. The seal assembly 36 is a stationary component that forms a portion of a hot gas path between the rows of vanes 18 at the locations of the rotating blades 20. The seal assembly 36 is commonly formed by a plurality of ring segments attached to the vane carrier 28. Each seal assembly 36 can substantially surround a row of blades 20 such that the tips 26 of the rotating blades 20 are in close proximity to the seal assembly 36. A clearance is usually defined between the tips 26 of the rotating blades 20 and an inner surface of the seal assembly 36. During engine operation, high temperature, high velocity gases flow through the rows of vanes 18 and blades 20 in the turbine section 16. It is desirable to keep the clearance as small as possible to increase engine performance because fluid leakage through the clearance contributes to system losses, decreasing the operational efficiency of the engine. However, it is necessary to maintain a clearance to prevent rubbing between the rotating blades 20 and stationary seal assembly 36 during operation of the engine.